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1. Introduction Recently, very small antennas are requested in RFID tags and tire attached sensors of the tire pressure monitoring system (TPMS). In these applications, normal-mode helical antennas (NMHA) are interested that can achieve high antenna efficiencies at very small size such as 1/100 wavelengths. Moreover, NMHA can increase antenna gains in the metal plate proximity use. However, NMHA have serious defect of very narrow bandwidths in very small sizes. In order to expand bandwidths, employing additional antennas are often considered. In this paper, employment of folded structures with NMHA is studied. In studying antenna electrical characteristics, electromagnetic simulations are conducted. As for folded structures, antenna input impedances increases of NMHA were studied [1]. However, effects on bandwidths were not shown. Therefore, band widths characteristics of a fundamental NMHA is studied at first. Then, calculated results of folded structures are shown.